The present invention relates to a new blend of polymers, its preparation and its application to the manufacture of components of electrochemical reactors. The invention relates in particular to the application of this blend of polymers to the manufacture of frames for alkaline electrolysis cells operating at a high temperature, in particular those intended to ensure the alkaline electrolysis of water.
The present invention permits the production of frames for the filter press stack of an electrolyzer intended, for example, to provide an alkaline electrolysis and more particularly the alkaline electrolysis of water at a high temperature.
The frames form the supporting structure of the electrolyzer and contain the electrolyte. They must ensure sealing leaktight to the liquid and to the gases evolved at an overpressure relative to the surrounding environment. They ensure the geometric location of the cell components, such as the electrodes and the diaphragm. In particular, they determine the spacing between these components.
In addition, the frames permit the circulation of fluids towards the interior and towards the exterior of the cells by means of accurately calibrated orifices. They thus ensure the distribution of the fluid at the entry and the collection of the emulsions at the exit.
Finally, the frames must ensure the electric insulation of the adjacent electrodes.
The whole combination of these functional characteristics must be maintained during the entire lifetime of the installation, in the aggressive environment formed by the concentrated, hot electrolyte (for example: 80,000 hours in 40% potassium hydroxide, at a temperature of the order of 120.degree. C., under an internal oxygen and hydrogen pressure of 30 to 60 bars).
In the present state of the technique, there is no industrial plant to be found which makes it possible to reach high temperatures of the order of 120.degree. C. in concentrated potassium hydroxide. Various solutions have, however, already been suggested for the production of such frames. They usually make use of fluorinated polymers whose many disadvantages rule out these solutions. In fact, fluorinated polymers having a high creep. Their industrial mass production by injection is found to be impracticable in the present state of the art, even for smaller dimensions than those which are under consideration. Their coefficient of expansion is an order of magnitude higher than that of the electrodes to be supported, which presents mechanical problems. The change in the geometry due to post-injection relaxation produces deformations which are incompatible with the function of a fluid injector.
The solution which is proposed within the scope of the present invention is based on the development of a blend of polymers. It involves blending, in the form of an adequate structure, a chemically non-reactive and hydrophobic fluorinated polymer with a matrix of a heat-stable polymer. The heat-stable polymer confers its mechanical properties to the compound, whilst the hydrophobic fluorinated polymer forms an anticorrosion barrier by stopping the penetration by the aggressive solution. The structure of the dispersion of fluorinated polymer in the matrix must be organized so that it behaves towards the aggressive agent as would a continuous phase of the same material, so as to form a surface screen, regardless of the orientation of the surface remaining facing the reactive environment.